UPPER SILURIAN. 249 



3. Arctic American Upper Silurian Species occurring elsewhere. 



Stromatopora concentrica, Great Britain, Eifel. 



Halysites catenulata. Great Britain, Norway, Sweden, Russia, United States. 



Favosites Gothlandica, Great Britain, Sweden, United States. 



Favosites polymorpha, Great Britain, France, Belgium, Eifel. 



Receptaculites Neptuni, Great Britain, Belgium, Eifel, United States. 



Orthis elegantula, Great Britain, Gothland, Russia, United States. 



Atrypa reticularis, Great Britain, Gothland, Urals, Altai in Siberia, United States. 



Pentamerus conchidium Dalman, Gothland. 



Rhynchonella (?) sublepida(f) De Verneuil, Urals. 



Encrinurus leris (?) Angelin, Gothland. 



Leperditia Baltica Hisinger, Gothland. 



A considerable number of species in the British Lower Silurian pass into the Upper 

 Silurian. They are found mingled in the intermediate Llandovery formations ; which, 

 although classed with the Upper Silurian, contain between 40 and 50 species that occur 

 also below. 



Barrande has found nearly 2,800 species of fossils in the Bohemian Silurian basin, 

 including the Primordial strata. The limestone E abounds in organic remains ; and 

 among them are 400 species of Cephalopods, and 183 species of Trilobites (of the genera 

 Calymene, Acidaspis, Ceraurus, Cyphaspis, Lichas, Phacops, Harpes, Bronteus, and 

 Proetus). Barrande regards this as the culminating period for the Trilobite race. Lime- 

 stone F also contains 88 species of Trilobites, and of the same genera, associated with a 

 profusion of Brachippods. In G, there are many Goniatites and other species, which 

 show that, while the strata are intimately connected with E and F physically, and in 

 their fossils, the period probably corresponds in part with the early Devonian. Besides 

 56 species of Trilobites of the above genera, there are others of the Devonian genus 

 Dalmanites. In Bohemia, 57 Lower Silurian species pass into the Upper Silurian. 



A list of the genera common to the American and European continents would show 

 almost a complete identity, and the same system of progress from the Lower Silurian 

 onward. In each, the genera Spirifer and Chonetes, among the Brachiopods, were 

 added to Orthis, Leptcena, and Atrypa; Halysites (Chain-corals), Favosites, and Cyatho- 

 phyllklm became abundant; Crinoids were greatly multiplied ; and the Eurypterus group, 

 or Cyclopoid Crustaceans, commenced a new line among the Articulates; while Grap- 

 tolites, so common in the Lower Silurian, were few in species and numbers. 



The number of Silurian species described, up to 1872, according to Barrande, is as 

 follows : — 



Sponges and other Protozoans . 153 Bryozoans 478 



Polyp Corals 718 Brachiopods 1,567 



Echinoderms (Crinoids, etc.) . . 588 Lamellibranchs 1,086 



Worms 185 Heteropods and Pteropods . . 390 



Trilobites 1,579 Gasteropods 1,316 



Other Crustaceans ( including Cephalopods 1,622 



some Cirripeds) 348 Fishes 40 



Which, with 4 of uncertain relations, make in all 10,074 species. 



3. OBSERVATIONS ON THE UPPER SILURIAN. 



1. General features. — Fresh-water lakes and rivers, fresh-water de- 

 posits, and land or fresh-water animal life, continue unknown through 

 the American records of the Upper Silurian, as thus far investigated. 

 Such rivers and lakes probably existed, as it is certain there was dry 

 land ; but they have left nothing that survived subsequent changes. 



